1. Field of the Invention
This invention relates to an acoustic touchscreen constructed directly on a cathode ray tube, and methods therefor.
2. Description of Related Art
An acoustic touchscreen has a touch-sensitive area on which the occurrence and location of a touch is sensed via the touch's effect on the transmission of acoustic waves thereacross. A common type of acoustic touchscreen employs Rayleigh waves (a term which, as used herein, subsumes quasi-Rayleigh waves). Illustrative disclosures relating to Rayleigh wave touchscreens include Adler, U.S. Pat. No. 4,642,423 (1987); U.S. Pat. No. 4,645,870 (1987); U.S. Pat. No. 4,700,176 (1987); U.S. Pat. No. 4,746,914 (1988) (hereinafter "Adler '914"); U.S. Pat. No. 4,791,416 (1988); and Re 33,151 (1990); Adler et al., U.S. Pat. No. 4,825,212 (1989); U.S. Pat. No. 4,859,996 (1989); and U.S. Pat. No. 4,880,665 (1989); Brenner et al., U.S. Pat. No. 4,644,100 (1987); Davis-Cannon et al., U.S. Pat. No. 5,739,479 (1998); and Kent, U.S. Pat. No. 5,708,461 (1998) and U.S. Pat. No. 5,854,450 (1998). Acoustic touchscreens employing other types of acoustic waves such as Lamb or shear waves, or combinations of different types acoustic waves (including combinations involving Rayleigh waves) are also known, illustrative disclosures including Kent, U.S. Pat. No. 5,591,945 (1997) and U.S. Pat. No. 5,854,450 (1998); Knowles, U.S. Pat. No. 5,072,427 (1991); U.S. Pat. No. 5,162,618 (1992); U.S. Pat. No. 5,177,327 (1993); U.S. Pat. No. 5,243,148 (1993); U.S. Pat. No. 5,329,070 (1994); and U.S. Pat. No. 5,573,077; and Knowles et al., U.S. Pat. No. 5,260,521 (1993). The documents cited in this paragraph are incorporated herein by reference.
FIG. 1 illustrates the operation of a typical acoustic touchscreen 1, having an active, or touch-sensitive area 2. A first transmitting transducer 3a is positioned outside of touch-sensitive area 2, acoustically coupled to the surface of touchscreen 1, and sends an acoustic signal in the form of an acoustic wave 11a traveling parallel to the top edge of touchscreen 1 and generally in the plane of touchscreen 1 . Aligned in the transmission path of acoustic wave 11a is a linear array of partially acoustically reflective elements 4a, each of which partially reflects (by approximately 90.degree.) and partially transmits the acoustic signals, creating a plurality of acoustic waves (exemplarily 5a, 5b, and 5c) traveling vertically (parallel to the Y-axis) across touch-sensitive area 2. (The spacing of reflective elements 4a is variable to compensate for the attenuation of the acoustic signals with increasing distance from first transmitter 3a.) Acoustic waves 5a, 5b, and 5c, upon reaching the lower edge of touchscreen 1, are again reflected by approximately 90.degree. (arrow 11b) by another linear array of similarly partially acoustically reflective elements 4b towards a first receiving transducer 6a, where they are detected and converted to electrical signals for data processing. Along the left and right edges of touchscreen 1 are located a similar arrangement. A second transmitting transducer 3b generates an acoustic wave 12a along the left edge, and a linear array of partially acoustically reflective elements 4c creates therefrom a plurality of acoustic waves (exemplarily 7a, 7b, and 7c) traveling horizontally (parallel to the X-axis) across touch-sensitive area 2. Acoustic waves 7a, 7b, and 7c are redirected (arrow 12b) by yet another linear array of partially acoustically reflective elements 4d towards receiving transducer 6b, where they are also detected and converted to electrical signals.
If touch-sensitive area 2 is touched at position 8 by an object such as a finger or a stylus, some of the energy of the acoustic waves 5b and 7a is absorbed by the touching object. The resulting attenuation is detected by receiving transducers 6a and 6b as a perturbation in the acoustic signal. Analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates of position 8.
Those skilled in the art will appreciate that it is not essential to have two sets of transmitting/receiving transducers to make a touchscreen. The device of FIG. 1, without one set of transducers, will still function as a touchscreen, detecting the occurrence of a touch and providing limited location information (one of the coordinates). Or, a touchscreen can be designed with only two transducers by using a common transmit/receive transducer scheme, as disclosed in Adler '914 (FIG. 8).
In normal usage a housing 9, typically made of molded polymer, is associated with touchscreen 1. Housing 9 contains a bezel 10 that overlays touchscreen 1, concealing the transmitting and receiving transducers, the reflective elements, and other components, but exposing touch-sensitive area 2. This arrangement protects the concealed components from contamination and/or damage, presents a more aesthetically pleasing appearance, and defines the touch-sensitive area for the user.
A touchscreen may comprise a separate faceplate (typically made of glass, but other hard substrates may be used) overlaid on a display panel such as a cathode ray tube (CRT), a liquid crystal display (LCD), plasma, electroluminescent, or other type of display. Alternatively it has been proposed to construct a touchscreen directly on the glass surface of a CRT, so that the CRT surface is the touch-sensitive surface, Adler '914 discloses such a construction. A direct-on-CRT touchscreen construction is desirable because it eliminates a piece of glass or other material between the viewer and the CRT, increasing the perceived display brightness. Also, there are economic advantages in dispensing with the overlay glass and not having to modify CRT chassis to make room for the overlay glass.
FIG. 2a shows a conventional CRT 15 on which a touchscreen may be constructed. CRT 15 comprises two glass sections, a rear tapering section referred to as a funnel 28 and, in front thereof, a panel 27. In turn, panel 27 includes a substantially rectangular frontal region 16 on which an image is displayed and which, if a touchscreen is installed, also serves as touch-sensitive area 2. Ancillary features include mounting ears 18 for attaching the housing (not shown) and a protective steel implosion band 23.
Frontal region 16 typically is not truly flat, but curved to an extent varying from CRT to CRT, with the more expensive CRT's tending to be less curved. But, for general purposes and also for the purposes of this invention, frontal region 16 may be considered to be substantially planar and defining a plane. Panel 27 further has, outside of the viewing area (and the touch-sensitive area, if a touchscreen has been installed) and below frontal region 16, a shoulder region 17 where the glass curves down and away from the plane of frontal region 16. Shoulder region 17 includes corner regions 26 having complex non-Euclidean topography, at the confluences of the corners of frontal region 16 and shoulder region 17. The degree of curvature of CRT 15's glass surface in shoulder region 17 (including corner regions 26) may be quite high, compared to that of frontal region 16. The radius of curvature of frontal region 16 may be on the order of 50 centimeters or more, while shoulder region 17 may have much smaller radii of curvature, on the order of a few centimeters. Thus, transition 29 from frontal region 16 to shoulder region 17 may be defined as occurring where there is a sharp discontinuity (decrease) in the radius of curvature of the glass surface. If frontal region 16 is treated as being substantially planar, the plane perpendicular to the axis of the CRT and intersecting this discontinuity may be considered to be its plane.
In building a direct-on-CRT touchscreen, the touchscreen manufacturer normally does not manufacture the CRT itself. Rather, the manufacturer works with the CRT as supplied by a monitor manufacturer (or, in the case of a monitor integrated with a computer CPU chassis, such as the iMac computer from Apple Computer, from the computer manufacturer). Since it is often impractical for the touchscreen manufacturer to replace the supplied housing with a new housing, the manufacturer must adapt to whatever space is available between the supplied housing and the CRT for accommodating the touchscreen elements such as the transmitting and receiving transducers (collectively referred to as transducers) and the reflective elements. Even where the touchscreen manufacturer has design control over the bezel, mechanical interference with the transducers often force a reduction in the dimensions of the bezel opening that prevents one from utilizing the full available display area of the CRT.
Conventionally, touchscreen components are placed on the frontal region. FIG. 2b is a frontal view of the CRT 15 of FIG. 2a having transmitting and receiving transducers 3a, 3b, 6a and 6b and arrays of reflective elements 4a, 4b, 4c, and 4d mounted thereon, on frontal region 16 thereof. (A like arrangement is shown in FIG. 1 of Adler '914.)
Normally, there is sufficient clearance for the reflective elements, which have a low profile. However, installation of the transducers is a more difficult proposition, due to their higher profile. This problem is illustrated in FIG. 3. (Dotted line 13 denotes the plane of frontal region 16.) When housing 9 is mounted on CRT 15 (i.e., moves in the direction indicated by arrow A), there is mechanical interference between bezel 10 and transducer 4. This interference may impede the proper functioning of transducer 4 or, worse yet, 30 damage either transducer 4 or bezel 10. Sometimes it is possible to create sufficient clearance by carving out a small amount of bezel material, but such a solution is not generically applicable and is anyway undesirable and/or impractical for a variety of reasons. The carving-out is a slow, labor-intensive operation; the bezel may be weakened and rendered susceptible to damage in subsequent use; and the carved out region may be visible, especially if the housing is made of translucent or transparent material.
Reference is also made to Davis-Cannon et al., U.S. Pat. No. 5,739,479 (1998), which discloses an acoustic touchscreen containing the transducers recessed on a beveled portion of the touchscreen. However, the invention there may not be applicable for a manufacturer installing touchscreens directly on a CRT surface, as conventional CRT's do not have such beveling. Reference is additionally made to Kambara et al., WO 98/29853 (1998), which discloses grating transducers for acoustic touchscreens. However, the piezoelectric elements of grating transducers must be placed on the underside of the touchscreen, an option not available for a direct-on-CRT construction.
Thus, it is desirable to develop a direct-on-CRT touchscreen construction which is compatible with tight clearances available between a CRT and its bezel and is adaptable for use with CRT's and housings as received from the CRT-monitor supplier, or which allows custom bezel designs maximizing the use of the CRT's display area.